Because Bethesda relies on players imagination to fill up the holes. They don't even think of most stuff people come up with to justify stuff in their games. They just get a few people sitting around a table and ask for suggestions. Then they implement some of those suggestions and usually don't care about consistency.

Isn't their entire endgame to replace humanity with synths and lord over them? Hard to tell considering how over the place they are in leadership. I get that Beth wanted to emulate the whole New Vegas thing where they have good writing but it doesn't translate well to the softcore Enclave clone in Fo4.